The purpose of the proposed research is to determine the developmental pattern of glucose transport systems in the intestinal epithelium of chick embryos and to ascertain the role of hormones in the maturation of these systems. Epithelial cells isolated from the embryonic intestine at 15, 17, 19, and 21 days of development and from specific levels of the intestinal villi in hatched chicks will be utilized to determine the developmental patterns of both the active and passive glucose transport systems. These studies will determine the overall ability of the cells to concentrate glucose, the affinity of the active and passive transport systems for glucose (Km), and the maximum glucose transport rate of each system (Vmax) during embryonic development and during migration of the immature epithelial cells from crypt to villus tip in intestine of hatched chicks. Additionally, the extent to which active glucose transport is influenced by ATP availability and/or (Na+ K+)-ATPase activity will be established. The glucose active and passive transport systems will be assayed independently of one another in whole cells by the appropriate use of specific inhibitors and by use of glucose analogues specific for each system. The potential regulatory role of hormones will be tested in an organ culture system. Embryonic intestine from 14-and 19-day-old embryos will be cultured for 2-4 days in the presence of individual hormones (thyroxine, hydrocortisone, insulin, and vitamin D) to determine whether active glucose transport can be induced in young intestine and whether hormones influence any of the above parameters of active or passive transport during embryonic development. The nature and molecular basis of changes in the active glucose transport system which occur during development will be further studied by utilizing microvillar membrane vesicles obtained from the epithelium of intact and cultured tissue. The proposed project has significance in the field of cell physiology, since a long range goal is to determine the mechanisms by which membrane transport systems differentiate. An analysis of the maturation of intestinal transport during fetal life is of interest to the medical field, since this approach can provide insight into the problems of malabsorption which may occur after birth. Since development of embryonic chick intestine closely resembles that of mammals, this system should serve as a useful model for the functional maturation of mammalian (and human) nutrient transport systems.